1. Technical Field
The present invention relates to an image formation method, a toner set, and a white toner.
2. Description of Related Arts
By an image formation method using an electrophotography system, firstly the surface of an image forming body is charged uniformly by a charging means, then image exposure is conducted to form an electrostatic latent image. The latent image part is developed by a subsequent developing means to form a toner image. In the field of toners for an electrostatic latent image used for image formation in the electrophotography system, developments have been carried out recently in response to various demands from the market. Especially, types of recording media for printing have been increasing, and broad applicability of a printing machine to such recording media is very strongly demanded by the market.
For example, when output is made onto a special recording medium, such as color paper or black paper, aluminum evaporated paper, and transparent film, since color characteristics of a recording medium have an influence, a full-color toner composed solely of 4 colors of yellow, magenta, cyan, and black, cannot sufficiently develop colors. Therefore, it has been proposed to use a white toner newly as the 5th color at the lowermost layer. By forming a white toner image, the hue of a recording medium can be masked, and disorder of an image caused by irregularity of a recording medium surface can be suppressed.
For masking the hue of a recording medium, it is necessary that such a part of a recording medium as corresponds to an image layer part formed by color toners is covered by an image layer formed by a white toner, and further that the toner contains such amount of white pigment as is adequate for masking. However, when the content of a pigment in a toner is increased, the amount of the white pigment exposed to a surface of the toner also increases to deteriorate the electrostatic chargeability, to cause possibly fogging (a phenomenon, in which a trace of toner is transferred to a part where it should not be printed by rights), and to decrease the image intensity in fixing.
To suppress such an image defect, Japanese Patent Application Publication No. 2007-33719 discloses a white toner, in which the contents of a crystalline resin and a white colorant are in specific ranges.